According to the Terms of Service, you cannot run a server on any Comcast residential account for the purpose of external usage. This includes FTP, HTTP, POP3/SMTP, telnet or any other service that users can access via the Internet.

You may set up any server you wish for your LAN.

*This FAQ is based on user knowledge from a volunteer core of BroadbandReports' members. This FAQ in no way constitutes official information from Comcast or any of its affiliates.